When using non-oriented magnetic steel sheet for a motor core or stationary apparatus, the core is made by slitting a magnetic steel sheet coil, punching it into predetermined shapes, stacking a predetermined number of these shapes, then clamping them by welding, calking, bolting, band clamping, molding, bonding, etc. In the case of using a transformer core made of a grain-oriented electrical steel sheet, the strip coil is slitted, cut or punched into a predetermined shape, and thereafter these shaped sheets are fabricated to stacked core or wound core. Transformers come in roughly three types:
1) Mainly medium-sized to large-sized “stacked transformers” having oriented magnetic steel sheet stacked to form a core
2) Small-sized “wound transformers” having oriented magnetic steel-sheet or amorphous metal wound to form a core
3) “Small-sized transformers” including switching power source attachments attached to apparatuses having mainly non-oriented magnetic steel sheet, oriented magnetic steel sheet, amorphous metal, and permalloy as stacked and wound cores (EI cores etc.)
Medium- and large-sized transformers called “stacked transformers” of 1) are transformers used in ultra-high voltage substations and primary substations to intermediate substations. They are produced by stacking oriented magnetic steel sheet and fastening them by bolts and nuts or special tape or if necessary annealing or varnishing and attaching windings.
Small-sized transformers called “wound transformers” of 2) are small-sized transformers for power distribution use positioned downstream of intermediate substations. They are assembled by winding slit oriented magnetic steel sheet and amorphous metal to a predetermined size, shaping this, then strain annealing, again shaping, then winding conductors.
The EI cores and other small-sized transformers attached to electrical apparatuses of 3) are not limited to oriented magnetic steel sheet and may also use non-oriented magnetic steel sheet. They are formed by cutting or punching the-sheet to predetermined sizes, then stacking. Sometimes they are also produced by winding.
Note that the above distinctions are peculiar to Japan. In other countries, particularly in Europe, there is no classification of 2). This is considered a small-size of the classification 1).
All transformers basically mainly use magnetic steel sheet or amorphous metal as the material for the core in order to secure efficiency.
Among these, magnetic sheel sheet is produced by steelmakers. The final form in the steelmakers is normally coiled steel sheet of a thickness of 0.20 mm to 0.70 mm. This is slit into the necessary width, then further cut into the necessary lengths and cut into the final sizes.
The surface of magnetic steel sheet is normally treated to give it an insulation coating. Varnishing and bluing are performed with the purpose of improving the corrosion resistance and insulation of the end faces of the core (surfaces formed by punching, cutting, etc.) The surface insulation coating of magnetic steel sheet used in this way has an effect on the corrosion resistance, punchability, weldability, and insulation. In particular, much research regarding improvement of the insulation has been performed from the viewpoint of improving the insulation between steel sheets at the time of stacking so as to suppress an increase in iron loss due to eddy current loss.
In the past, as the insulation coating agent for the surface of steel sheet, an organic type coating agent have been used in a grain-oriented electrical steel sheet, and an inorganic type, organic type, and composite inorganic-organic type coating agents have been used in non-oriented electrical steel sheet in accordance with the application of use or objective. An excellent heat resistant insulation film is required for a grain-oriented electrical steel sheet because forsterite film formed during secondary recrystallization annealing on the surface of the steel sheet and therefore heat-flattening treatment at 800–900° C. must be done to coil-set and to remove stress. In addition, a grain-oriented electrical steel sheet has a considerable improvement of iron loss and magnetic strain by film tensioning effect. As mentioned above, an organic type coating agent as the insulation coating is not suitable for a grain-oriented electrical steel sheet. In general, an inorganic type coating is superior in heat resistance and weldability, but inferior in punchability. On the other hand, an organic coating is superior in punchability and adhesiveness, but inferior in heat resistance and weldability. In recent years, to eliminate the defects in the two, composite inorganic-organic type coatings able to exhibit performance between the two have come into general use. With only the insulation coating formed at the time of producing the steel sheet, however, the insulation becomes insufficient or, in the case of including an annealing step, the insulation drops considerably, so varnishing or other insulation becomes necessary.
In particular, in recent years, it has been discovered that the insulation at the end faces of the core formed by punching or cutting has a large effect on the core efficiency. There has been rising demand for development of an industrially superior technique for treating the end faces of cores. With the method of insulation treatment of the end faces of cores used generally in the past, however, while considerably effective for improvement of the corrosion resistance or insulation, the adhesiveness, coating strength, and insulation have been insufficient.
For example, bluing not only results in poor insulation and corrosion resistance, but also inferior stability and gives rise to tremendous cost increases in the heat treatment step.
Further, treatment by an organic compound or a varnish comprised mainly of an organic compound is effective in its own right for corrosion resistance and insulation, but is insufficient for adhesiveness, coating strength, insulation, and heat resistance. In particular, the problem of poor wetability means that cleaning or annealing is required as pre-treatment. Further, for heat resistance as well, this is unsuitable when the process of formation of the core includes aluminum diecasting or other heat treatment.
Further, treatment by phosphate or another inorganic-type insulation coating, like treatment by organic type and semiorganic type coating, requires pre-treatment and requires high temperature drying. In coating performance as well, there are the problems that thick coating is difficult, the adhesiveness is poor, the insulation coating detaches due to annealing, etc. These prior art have had many problems from the viewpoint of the work environment and efficiency and further improvement is desired.
Further, phenol resin laminates, silicone resin laminates, molded phenol products, and other synthetic resin insulating materials are used as insulators, but these are not coated directly on the end faces of the cores, but are wound or adhered as finished products and therefore cannot prevent drops in insulation due to burrs etc. of the end faces.
Further, in recent years, transformers using amorphous metal as the material of the cores have also been produced, but in the production of the transformers, due to the “weak stiffness”, at the time of “core insertion (lacing)”, temporary fastening is performed due to the “tearing” of the amorphous foil. Measures for prevention of this “tearing” are necessary. The cores of the completed transformers are mainly dipped in oil, but the temporary fastening and fixing solution used for prevention of this “tearing” requires oil resistance. There are inherent limitations on the properties sought from the viewpoint of work efficiency and labor health.
As electrical apparatuses, there are motors, actuators, generators, transformers, reactors, and other electromagnetic apparatuses or heaters etc. Electromagnetic apparatuses are generally comprised of conductors for carrying a current and a magnetic circuit for carrying magnetic flux.
A large amount of current is passed through the conductors to achieve a high output of the electromagnetic apparatus. If a large current is passed through the conductors, however, the conductors or peripheral materials are heated, the electrical insulation of the conductors or magnetic materials is destroyed, and problems arise in fastening the members of the apparatuses.
The magnetic circuit uses a core and yoke. Most cores used are stacks of magnetic steel sheet. For bundling the stacked core, calking, welding, bolting, etc. are frequently used. With calking and welding, electrical short-circuits occur between the stacked layers. With AC excitation, a short-circuiting current is produced and a drop in the performance-of the apparatus is caused. Therefore, sometimes molding or bonding is used for the bundling between magnetic steel sheets. With molding or bonding, however, use at a high temperature is not possible.
In a heater, the heating element is fastened and insulated by a ceramic or other member able to breakdown a high temperature. This fastening is partial. Time and labor are required for the assembly process and sometimes noise and vibration become problems due to the partial fastening. With bonding etc., complete fastening is possible. If insulation could be secured, the process would become simple and automation would also become possible, but at the present time, there is no method of bonding able to be used at a high temperature.